Jason, For the best answer to your question about shipping sidelock guns into Canada;
1. Phone the federal firearms registration program. If you get an affirmative answer,and you should, get the persons name, title, and contact phone #. Hang on to it.
2. Phone Canada Customs and ask the same question. You should get the same affirmative answer. If you do, get the persons name, title, & contact phone number. Hang on to this one too.
Most of the time there will be no problem getting a muzzleloader accross the border. Some times a rookie or someone with a burr under their saddle will do their best to be difficult. The names above will be the people you can name-drop if you have difficulty getting a muzzleloader into Canada.
If you are getting a percussion rifle,(long gun) you will need to have a PAL. It will have to be registered.
A flintlock rifle (longgun) is less of a problem. I'm not sure about the PAL requirement, but it does not need to be registered.
Notice, I only mentioned long guns. Pistols of any kind are restricted & really aren't worth the hassle.
Most of the dealers in the US will be used to shipping to Canada, & will know what has to be done.
Paul
P.S. Those of you who live in the states, please, save your breath. I'm fully aware of what draconion rules we live under, up here, but it is the law & fairly easy to live with. Perhaps, eventually, more reasonable heads will prevail and this law will go away.